1. Field of the Invention
The present invention involves systems and methods for remotely operating, administering, and maintaining physical links in a network that carries packet switched data.
2. Description of the Related Art
A data network typically is comprised of a plurality of hosts that communicate over an infrastructure. The infrastructure may include fiber, electrical, or wireless links, and network assemblies such as switches, routers, and media converters, among other things. A unit on the network is commonly and generically called a box, with each box having at least one of an egress port to the network and an ingress port from the data network. Types of data networks include, for instance, local area networks (LAN), metropolitan area networks (MAN), and wide area networks (WAN). A collection of interconnected networks is an internetwork or internet.
Most data networks are organized as a series of layers (also called levels), one built on the one below it. The purpose of each layer is to offer certain services to the higher layers, and to shield those higher layers from the details of how the offered services are actually implemented. The number of layers, the name of each layer, the contents of each layer, and the function of each layer vary from network to network. A layer n in one network device communicates with a corresponding layer n (a “peer” layer) in another network device according to a protocol.
A protocol is a language that is understood between parties that converse the same way. An example of a protocol is TCP/IP. A set of layers and protocols is a network architecture. A list of protocols used by a certain data network is a protocol stack.
In reality, no data are directly transferred from the layer n on one network device to the layer n on another network device. Instead, each layer passes data and control information to the layer immediately below it until the lowest layer is reached. Protocols that converse at a certain layer also terminate at that layer, but agnostically use protocols in lower layers as a transport means. Below the lowest layer is the physical transmission medium through which the actual communication occurs. Between each pair of adjacent layers is an interface. The interface defines which primitive operations and services the lower layers offer to the upper one.
An example of a network architecture is the OSI (Open Systems Interconnection) model. The OSI model includes seven layers, as shown in FIG. 1. Layer 1, the physical (PHY) layer, is the lowest layer. Generally, the PHY layer is concerned with serially transmitting and receiving data over the physical transmission medium, recovering the embedded clock, applying any coding or scrambling to the data stream, and aligning the data containers for use by the next upper layer, the Data Link Layer (DLC).
The DLC layer is responsible for maintaining the data link between the communicating systems. The DLC includes two sublayers: the Medium Access Control (MAC) sublayer and the Logical Link Control (LLC) sublayer. The MAC sublayer functions include framing and deframing data units, performing error checking, and acquiring the right to use the underlying physical medium where there is contention for bandwidth. The MAC sublayer makes a decision, based on proper order, frame length, and error checking whether received data is to be passed to the next upper layer. The LLC sublayer functions include initiation of control signal interchange, organization of data flow, interpretation of received command protocol data units (PDUs) and generation of appropriate response PDUs, and actions regarding error control and error recovery functions in the LLC sublayer.
Layer 3 of FIG. 1, the network layer, is responsible for an end to end addressing scheme for interconnecting a variety of networks, and fragmentation of data packets when the length of the packet is limited by an intermediate network. Layer 4, the transport layer, is responsible for an end to end accounting (where desired) for data packets and a connection into the application, e.g., HTTP, FTP, and SMTP. Layer 5, the session layer, allows users on different hosts to establish sessions between them. Layer 6, the presentation layer, is concerned with the syntax and semantics of the information transmitted. Finally, layer 7, the application layer, is application dependent, and provides a pathway to the application.
The Institute of Electrical and Electronic Engineers (IEEE), a professional standards organization, has developed a family of standards for LANs and MANs known as the IEEE 802 standards, which are well known and are incorporated herein by reference in their respective entireties. One of those standards, known as the IEEE 802.3 standard (incorporated herein by reference in its entirety), establishes a frame structure for data transmitted over the physical transmission medium.
FIG. 2 shows the nine fields of a typical frame in accordance with the IEEE 802.3 standard. The nine fields include a preamble field of up to seven bytes, each containing the bit pattern 10101010. The next field, the start of frame delimiter, is set to the sequence 10101011, and indicates the start of a frame. Next are fields of six bytes each for the destination and source addresses. The length field indicates how many bytes are present in the data field, which follows. The pad field is used to fill out the frame to a minimum size. The frame check sequence field (FCS) includes a four-byte cyclic redundancy check (CRC) value that is a function of the contents of all data symbols in the frame, excluding the preamble. Finally, there may be an extension field. Between every frame is a gap, which is sized to correct for clock differences between a transmitter and a receiver. A typical gap is 96 bit times. An idle (IDL) signal is transmitted in the gap. The IDL signals exist at the PHY layer only. The MAC sublayer of the DLC does not accept or use the IDL signals.
Operating, administering, and maintaining the physical transmission links between devices (e.g., at a control point and at an end user) in a data network is a key concern of those who own, manage, and use data networks. For instance, FIGS. 3A and 3b are simple examples of links between a service provider 20 (here, the control point) and one or more subscribers 22 (here, the end points). The service provider may be, for example, an Internet service provider or a telephone company that provides access to a larger network. The subscriber may be a business that has an internal LAN, or an individual in a home. The data network of FIG. 3A includes a point-to-point link between the service provider 20 and the subscriber 22. The actual physical links controlled by service provider 20 include a fiber optic link 24 between service provider 20 and a media converter 28, and an electrical link 26, which may be a twisted pair of copper wires or coaxial cable, between media converter 28 and subscriber 22. For instance, electrical link 26 may be an xDSL or regular Ethernet connection over Category 5 cabling. In FIG. 3B, the data network includes multiple subscribers 22. A fiber optic link 24 is linked between service provider 20 and a switch 30 to which the plural subscribers 22 are connected by separate electrical links 26.
Assume that a problem occurs with the connection between the service provider 20 and the subscriber 22 in the exemplary data networks of FIGS. 3A and 3B. The service provider 20 can run a loopback check that tests the network up to a demarcation point between service provider 20 and subscriber 22. If a problem is found during the loopback check, then service provider 20 will seek to identify a hasty repair. If no problems are found, then the problem is isolated to subscriber 22. If the subscriber 22 fails to isolate the problem further, however, there may be a dispute between the service provider 20 and the subscriber 22 as to who is responsible for identifying and fixing the problem. Typically, the service provider 20 must send a maintenance person to the demarcation point at subscriber 22's site, which can involve a significant expense of time and money. Even then, however, the subscriber 22 may develop a feeling of poor customer service on the part of the service provider 20. Clearly, it would be in the interest of those who operate, administer, and maintain data networks to be able to operate, administer, and maintain the entire physical transmission link between the service provider and the subscriber by automatic means, such that any problems in the physical transmission links or at intermediate points in the data network up to the demarcation point can be quickly and specifically identified, or problems may be conclusively identified as being beyond the demarcation point.